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 $106.84   11.814%   $119.4621   $119.46   $119.45   $119.50  
  Purchase #2 $168.87   7.219%   $181.0607   $181.06   $181.05   $181.10  
  Purchase #3 $52.55   8.330%   $56.9274   $56.93   $56.95   $56.90  
  Purchase #4 $156.52   6.823%   $167.1994   $167.20   $167.20   $167.20  
  Purchase #5 $229.60   6.449%   $244.4069   $244.41   $244.40   $244.40  
  Purchase #6 $66.91   11.840%   $74.8321   $74.83   $74.85   $74.80  
  Purchase #7 $198.92   10.618%   $220.0413   $220.04   $220.05   $220.00  
  7 purchase totals = $980.21       $1,063.9299   $1,063.93   $1,063.95   $1,063.90