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 $172.94   13.275%   $195.8978   $195.90   $195.90   $195.90  
  Purchase #2 $106.80   6.410%   $113.6459   $113.65   $113.65   $113.60  
  Purchase #3 $222.52   5.257%   $234.2179   $234.22   $234.20   $234.20  
  Purchase #4 $111.46   7.619%   $119.9521   $119.95   $119.95   $120.00  
  Purchase #5 $223.60   9.829%   $245.5776   $245.58   $245.60   $245.60  
  Purchase #6 $67.57   9.766%   $74.1689   $74.17   $74.15   $74.20  
  Purchase #7 $39.46   9.551%   $43.2288   $43.23   $43.25   $43.20  
  7 purchase totals = $944.35       $1,026.6890   $1,026.70   $1,026.70   $1,026.70