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 $177.43   5.174%   $186.6102   $186.61   $186.60   $186.60  
  Purchase #2 $181.52   11.514%   $202.4202   $202.42   $202.40   $202.40  
  Purchase #3 $190.50   7.642%   $205.058   $205.06   $205.05   $205.10  
  Purchase #4 $94.84   7.585%   $102.0336   $102.03   $102.05   $102.00  
  Purchase #5 $55.36   12.276%   $62.156   $62.16   $62.15   $62.20  
  Purchase #6 $40.96   11.438%   $45.645   $45.65   $45.65   $45.60  
  Purchase #7 $120.27   5.771%   $127.2108   $127.21   $127.20   $127.20  
  7 purchase totals = $860.88       $931.1338   $931.14   $931.10   $931.10