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 $87.35   5.289%   $91.9699   $91.97   $91.95   $92.00  
  Purchase #2 $67.84   11.508%   $75.647   $75.65   $75.65   $75.60  
  Purchase #3 $105.58   11.384%   $117.5992   $117.60   $117.60   $117.60  
  Purchase #4 $214.55   5.573%   $226.5069   $226.51   $226.50   $226.50  
  Purchase #5 $154.48   7.289%   $165.74   $165.74   $165.75   $165.70  
  Purchase #6 $118.35   3.159%   $122.0887   $122.09   $122.10   $122.10  
  Purchase #7 $36.45   11.325%   $40.578   $40.58   $40.60   $40.60  
  7 purchase totals = $784.60       $840.1297   $840.14   $840.15   $840.10