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 $92.74   12.152%   $104.0098   $104.01   $104.00   $104.00  
  Purchase #2 $137.65   10.484%   $152.0812   $152.08   $152.10   $152.10  
  Purchase #3 $89.69   7.713%   $96.6078   $96.61   $96.60   $96.60  
  Purchase #4 $145.34   7.263%   $155.896   $155.90   $155.90   $155.90  
  Purchase #5 $169.79   4.418%   $177.2913   $177.29   $177.30   $177.30  
  Purchase #6 $188.43   4.773%   $197.4238   $197.42   $197.40   $197.40  
  Purchase #7 $205.92   3.338%   $212.7936   $212.79   $212.80   $212.80  
  7 purchase totals = $1,029.56       $1,096.1035   $1,096.10   $1,096.10   $1,096.10