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 $70.93   10.110%   $78.101   $78.10   $78.10   $78.10  
  Purchase #2 $156.95   12.120%   $175.9723   $175.97   $175.95   $176.00  
  Purchase #3 $24.96   12.787%   $28.1516   $28.15   $28.15   $28.20  
  Purchase #4 $172.52   5.251%   $181.579   $181.58   $181.60   $181.60  
  Purchase #5 $150.76   3.650%   $156.2627   $156.26   $156.25   $156.30  
  Purchase #6 $232.53   12.449%   $261.4777   $261.48   $261.50   $261.50  
  Purchase #7 $203.73   4.163%   $212.2113   $212.21   $212.20   $212.20  
  7 purchase totals = $1,012.38       $1,093.7556   $1,093.75   $1,093.75   $1,093.90