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 $77.46   8.697%   $84.1967   $84.20   $84.20   $84.20  
  Purchase #2 $138.27   5.490%   $145.861   $145.86   $145.85   $145.90  
  Purchase #3 $70.95   5.745%   $75.0261   $75.03   $75.05   $75.00  
  Purchase #4 $182.68   5.388%   $192.5228   $192.52   $192.50   $192.50  
  Purchase #5 $151.48   10.139%   $166.8386   $166.84   $166.85   $166.80  
  Purchase #6 $170.60   6.515%   $181.7146   $181.71   $181.70   $181.70  
  Purchase #7 $27.97   4.320%   $29.1783   $29.18   $29.20   $29.20  
  7 purchase totals = $819.41       $875.3381   $875.34   $875.35   $875.30