Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $12.78   8.310%   $13.842   $13.84   $13.85   $13.80  
  Purchase #2 $175.45   3.458%   $181.5171   $181.52   $181.50   $181.50  
  Purchase #3 $216.64   13.637%   $246.1832   $246.18   $246.20   $246.20  
  Purchase #4 $107.44   10.510%   $118.7319   $118.73   $118.75   $118.70  
  Purchase #5 $228.87   7.229%   $245.415   $245.42   $245.40   $245.40  
  Purchase #6 $147.49   8.840%   $160.5281   $160.53   $160.55   $160.50  
  Purchase #7 $113.41   10.140%   $124.9098   $124.91   $124.90   $124.90  
  7 purchase totals = $1,002.08       $1,091.1271   $1,091.13   $1,091.15   $1,091.00